In general, polyesters such as polyethylene terephthalate are possessed with good chemical stability, physical and mechanical strength, heat resistance, chemical resistance and electrical insulation property; and, therefore, have been used for preparing various articles including magnetic tapes, photographic film, electrical insulating materials, capacitors and wrapping materials.
However, such polyester films are liable to generate and accumulate static electricity due to their high dielectricity; and, as a result, there may arise several problems in connection with, e.g., their preparation, printing and/or wrapping process: that is, they tend to adhere to a processing roll or among themselves; to create electric shock or spark; and to contaminate the surface of the film easily by way of attracting dusts. Moreover, the state of printing and coating onto the film tends to become non-uniform due to their generally poor receptivity to ink or coating compositions.
To solve the above-mentioned problems, many attempts have been made. For instance, to improve the antistatic property, an antistatic agent has been incorporated into a polyester film by way of, e.g., impregnating polyester with a polyalkylene glycol or a mixture of a polyalkylene glycol and a metallic sulfonate derivative. Japanese Patent Publication No. 12910/1983 discloses a biaxially oriented polyester film incorporated with polyethylene glycol and a metallic sulfonate derivative. Also, Japanese Patent Publication No. 15148/1984 describes a polyester composition formulated with a styrene oligomer and a metallic alkylsulfonate. However, such antistatic additives are not normally dispersed or mixed well in the polyester composition, which makes the antistatic property of the polyester film non-uniform. Further, the presence of such antistatic agents often deteriorates the clarity, mechanical property and/or surface tension of the film, thereby adversely affecting the coating or printing process of the film.